Regulation of neurotransmitter release in an identified synapse in the abdominal ganglion of Aplysia californica. We have been studying an identified synapse which responds to a train of stimuli with depression followed by facilitation and post tetanic potentiation. Having shown that the sequence of phenomena is due to alterations in transmitter release we have identified a number of other transmitters and pharmacological agents which regulate specific aspects of transmitter release. These agents include acetylcholine, dopamine, 5- hydroxyltryptamine, trimethidinium and morphine. We propose to use these agents to help elucidate mechanisms of regulation of transmitter release in response to a train of stimuli. Agglutinins from slime mold and embryonic chick brain. We have identified soluble proteins from embryonic chick brain and also from a number of species of slime mold which agglutinate erythrocytes. Present evidence indicates that the slime mold proteins play a specific role in cell aggregation. We propose to continue purification characterization of these proteins and to further study their interaction with cell surfaces.